U.S. patent number 5,604,963 [Application Number 08/546,938] was granted by the patent office on 1997-02-25 for hook structure for molded surface fastener.
This patent grant is currently assigned to YKK Corporation. Invention is credited to Mitsuru Akeno.
United States Patent |
5,604,963 |
Akeno |
February 25, 1997 |
Hook structure for molded surface fastener
Abstract
In a hook structure for a molded surface fastener, in an
arbitrary cross section of each of a stem and a hook-shape engaging
portion of a hook, the cross-sectional area is divided into front
and rear side cross-sectional areas with respect to the center line
of the hook, and the front side cross-sectional area is defined to
be larger than the rear side cross-sectional area. Therefore, the
neutral plane of the hook is shifted toward the front side of the
stem and the inner side of the hook-shape engaging portion to a
further extent than conventional to reduce possible tensile
stresses in the front part of the stem and the inner part of the
hook-shape engaging portion so that, as compared to the
conventional hook made of the same resin quantity and having a
substantially similar shape, the strength of the hook is increased
sharply and, necessarily, both the front part of the stem and the
inner part of the hook-shape engaging portion is increased in
rigidity as compared to the other part and hence is difficult to
deform, thus causing an increased strength as well as an increased
engaging strength with a loop of a companion surface fastener.
Inventors: |
Akeno; Mitsuru (Toyama-ken,
JP) |
Assignee: |
YKK Corporation (Tokyo,
JP)
|
Family
ID: |
17316266 |
Appl.
No.: |
08/546,938 |
Filed: |
October 23, 1995 |
Foreign Application Priority Data
|
|
|
|
|
Oct 24, 1994 [JP] |
|
|
6-258153 |
|
Current U.S.
Class: |
24/452; 24/442;
24/449; 428/100 |
Current CPC
Class: |
A44B
18/0061 (20130101); Y10T 24/2767 (20150115); Y10T
24/2792 (20150115); Y10T 24/27 (20150115); Y10T
428/24017 (20150115) |
Current International
Class: |
A44B
18/00 (20060101); A44B 018/00 () |
Field of
Search: |
;24/452,442,446,447,448,449,450,451 ;428/100 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Brown; Peter R.
Assistant Examiner: Tran; Hank V.
Attorney, Agent or Firm: Hill, Steadman & Simpson
Claims
What is claimed is:
1. A hook structure for a molded surface fastener comprising:
a substrate sheet; and
a multiplicity of hooks molded on and projecting from one surface
of said substrate sheet,
each of said hooks is composed of a stem, which has a rear surface
rising obliquely in a smooth curve from said substrate sheet and a
front surface rising upwardly from said substrate sheet, and a
hook-shape engaging portion extending forwardly from a distal end
of said stem, said hook shape engaging portion having an upper
surface and a lower surface, and
wherein a first transverse cross section of said stem of each of
said hooks in a plane taken parallel to the surface of said
substrate sheet has a first cross-sectional area divided into front
and rear side cross-sectional areas with rerspect to a transverse
line located midway between said front and rear surfaces, said
front side cross-sectional area is larger than said rear side
cross-sectional area, and
wherein a second transverse cross section of said hook-shape
engaging portion of each of said hooks taken in a plane which is
perpendicular to said lower surface has a second cross sectional
area divided into upper and lower side cross-sectional areas with
respect to a transverse line located midway between said upper and
lower surfaces, said lower side cross-sectional area is larger than
said upper side cross-sectional area.
2. A hook structure according to claim 1, wherein each of said
first and second transverse cross sections has a generally
trapezoidal shape.
3. A hook structure according to claim 1, wherein each of said
first and second transverse cross sections has a shape analogous to
the longitudinal cross section of an egg.
4. A hook structure according to claim 1, wherein each of said
first and second transverse cross sections has a generally U
shape.
5. A hook structure according to claim 1, wherein each of said
first and second transverse cross sections has a generally inverted
T shape.
6. A hook structure according to claim 1, wherein each of said
first and second transverse cross sections has a generally
criss-cross shape.
7. A hook structure according to claim 1, wherein each of said
first and second transverse cross sections has a generally
triangular shape.
8. A hook structure according to claim 1, wherein said second cross
sectional area and said first cross sectional area are gradually
increasing taken from a tip of said hook-shape engaging portion to
a base of said stem.
9. A hook structure according to claim 1, wherein each of said
hooks has a reinforcing rib on at least one side surface of said
stem.
10. A hook structure for a molded surface fastener comprising:
a substrate sheet; and
a multiplicity of hooks molded on and projecting from one surface
of said substrate sheet,
each of said hooks is composed of a stem, which has a rear surface
rising from said substrate sheet and a front surface rising
upwardly from said substrate sheet, and a hook-shape engaging
portion extending forwardly from a distal end of said stem, said
hook shape engaging portion having an upper surface and a lower
surface, and
wherein a first transverse cross section of said stem of each of
said hooks taken in an arbitrary plane parallel to the surface of
said substrate sheet has a first cross sectional area, and the
first transverse cross section is shaped such that when said first
cross sectional area is divided into front and rear side
cross-sectional areas with respect to a transverse line located
midway between said front and rear surfaces, said front side
cross-sectional area is larger than said rear side cross-sectional
area, and
wherein a second transverse cross section of said hook-shape
engaging portion of each of said hooks taken in an arbitrary plane
which is perpendicular to said lower surface has a second
transverse cross sectional area, and the second transverse cross
section is shaped such that when said second cross sectional area
is divided into upper and lower side cross-sectional areas with
respect to a transverse line located midway between said upper and
lower surfaces, said lower side cross-sectional area is larger than
said upper side cross-sectional area.
11. A hook structure according to claim 10, wherein each of said
first and second transverse cross sections has a generally
trapezoidal shape.
12. A hook structure according to claim 10, wherein each of said
first and second transverse cross sections has a shape analogous to
the longitudinal cross section of an egg.
13. A hook structure according to claim 10, wherein each of said
first and second transverse cross sections has a generally U
shape.
14. A hook structure according to claim 10, wherein each of said
first and second transverse cross sections has a generally inverted
T shape.
15. A hook structure according to claim 10, wherein each of said
first and second transverse cross sections has a generally
criss-cross shape.
16. A hook structure according to claim 10, wherein each of said
first and second transverse cross sections has a generally
triangular shape.
17. A hook structure according to claim 10, wherein said second and
first transverse cross sections are gradually increasing from a tip
of said hook-shape engaging portion to a base of said stem.
18. A hook structure according to claim 10, wherein each of said
hooks has a reinforcing rib on at least one side surface of said
stem.
19. A hook structure according to claim 10, wherein said rear
surface is a smooth obliquely rising surface from said substrate.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a molded surface fastener in which a
multiplicity of hooks are molded on a substrate sheet by extrusion
or injection molding of thermoplastic synthetic resin, and more
particularly to a hook structure in which hooks to be molded of the
same quantity of resin are improved in engaging strength and
durability.
2. Description of the Related Art
Surface fasteners of the type in which hooks are formed by weaving
monofilaments in a woven cloth so as to form loop piles of
monofilaments and then cutting the loop piles are well known in the
art. This type surface fastener has softness of a woven cloth and
softness of monofilament and is characterized in that the hooked
surface fastener comes into engagement with and are peeled off
loops of a companion surface fastener with a very smooth touch.
Moreover, since the monofilaments constituting the hooks are
treated by drawing, the surface fastener is excellent in pulling
strength and bending strength even in a small cross-sectional area.
Further, since the surface fastener can have a very high density of
hooks depending on the woven structure, it is possible to secure a
high engaging rate and an adequate degree of durability. However,
with the woven type surface fastener, since consumption of material
and a number of processing steps are large, it is difficult to
reduce the cost of production.
For an improvement, a molded type surface fastener was developed in
which a substrate sheet and hooks are formed integrally and
simultaneously by extrusion or injection molding. Typical examples
of molding technology for this type surface fastener are disclosed
in, for example, U.K. Patent No. 1319511 and WO 87/06522. As a
rotary drum in which a number of molding disks each having on an
outer peripheral edge of each of opposite surfaces a number of
hook-forming cavities and a number of spacer disks each having flat
surfaces are alternately superimposed one over another is rotated,
molten synthetic resin material is forced against its peripheral
surface to fill the cavities and then the hooks formed in the
cavities are removed off the drum along with the substrate sheet.
The spacer disks are disposed between the molding disks because the
cavities of the whole shape of the hooks cannot be made in one mold
due to the shape of the hooks.
However, in the molded type surface fastener, partly since a
delicate shape cannot be obtained as compared to the woven type
surface fastener due to technical difficulty in molding process,
and partly since the formed hooks are poor in orientation of
molecules, only a very low degree of strength can be achieved with
the same size of the above-mentioned monofilament hooks. Therefore
none of the conventional molded type surface fasteners are
satisfactory for practical use. Further, according to the
conventional hook structure, the individual stem is simple in
cross-sectional shape and would hence tend to fall flat from its
base. As a result, the individual stems would not restore their
original posture after repeated use, thus lowering the rate of
engagement with loops of a companion surface fastener. Therefore,
in order to secure desired strength, it is absolutely necessary to
increase the size of the individual hooks, which makes the hooks
rigid and the number of hooks per unit area (density of hooks)
reduced to lower the rate of engagement with the companion
loops.
As a solution, a new hook structure which enables a smooth touch,
with the stem hardly falling flat, during the engaging and peeling
operation likewise the woven type surface fastener and which
increases the rate of engagement to secure adequate strength is
disclosed in, for example, U.S. Pat. No. 5,131,119. In the molded
type surface fastener disclosed in this U.S. Patent, each hook has
a hook-shape engaging portion extending forwardly from the distal
end of a stem which has a rear surface rising obliquely in a smooth
curve from a substrate sheet and a front surface rising upwardly
from the substrate sheet, and a reinforcing rib projecting from a
side surface of the stem, the cross-sectional area of the hook
increasing gradually from a tip of the hook-shape engaging portion
toward the base of the stem. The reinforcing rib serves to prevent
the stem from falling laterally and also to minimize the size of
the stem and the hook-shape engaging portion, maintaining a
required degree of engaging strength to the stem and the hook-shape
engaging portion.
According to the conventional molded hook structure, it is totally
silent about the transverse cross-sectional shape. Also in the
above-mentioned prior art references, the respective molded hook
structure has merely a triangular, a rectangular or a circular
(including an oval) transverse cross-sectional shape. Therefore in
the transverse cross-sectional shape taken along a plane
perpendicular to the axis (center line) of the hook, the
cross-sectional area is divided into front and rear cross-sectional
areas with respect to the center line, and the rear side
cross-sectional area is set to be equal to or larger than the front
side cross-sectional area in either the stem or the hook-shape
engaging portion. This means that the center of figure is located
on the center line or the rear side of the hook.
When the molded hook is disengaged from the loop of the companion
surface fastener, a tensile stress occurs inside the front part of
the hook with respect to its neutral line while a compressive
stress occurs inside the rear part of the hook. In general, this
type hook of synthetic resin is resistant against a compressive
stress but is remarkably less resistant to a tensile stress
compared to a hook of rigid material. Accordingly, in the case of
the conventional cross-sectional shape, small hooks in particular
are not only too low in strength but also high in flexibility, so
that the force of engagement with loops is remarkably lowered. When
hooks having large transverse cross-sectional area are disengaged
from loops, they would tend to be broken or damaged as the tensile
stress in the front part of the hook increases according to the
magnitude of the engaging force.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a hook
structure which can increase an engaging force compared to the
conventional hook structure, regardless of the size of the hook,
and can minimize a tensile stress which occurs inside the front
part of the hook.
According to this invention, the above-mentioned problems can be
solved by a hook structure for a molded surface fastener comprising
a substrate sheet and a multiplicity of hooks molded on and
projecting from one surface of the substrate sheet, wherein each of
the hooks is composed of a stem, which has a rear surface rising
obliquely in a smooth curve from the substrate sheet and a front
surface rising upwardly from the substrate sheet, and a hook-shape
engaging portion extending forwardly from a distal end of the stem.
And in each of a transverse cross section of the stem of each hook
along a line parallel to the surface of the substrate sheet and an
arbitrary transverse cross section including a normal line at a
lower surface of the hook-shape engaging portion, when the
cross-sectional area is divided into front and rear side
cross-sectional areas with respect to the center, the front
cross-sectional area is larger than the rear side cross-sectional
area.
The shape of-the above-mentioned cross sectional area can be
determined appropriately, but preferably, each transverse cross
section has a generally trapezoidal shape, a shape analogous to the
longitudinal cross section of an egg, a generally U shape, a
generally inverted T shape, a generally criss-cross shape, or a
triangular shape. Each hook has a varying cross-sectional area
gradually increasing from a tip of the hook-shape engaging portion
to a base of the stem. Further, each hook may have a reinforcing
rib on at least one side surface of the stem.
In operation, since the center line of figure is eccentrically
located toward the front side of the stem and the inner side of the
hook-shape engaging portion, the neutral plane of the hook is
shifted from the center line of figure toward the front side of the
stem and the inner side of the hook-shape engaging portion to
reduce possible tensile stresses which occurs in the front part of
the stem and the inner part of the hook-shape engaging portion so
that, as compared to the conventional hook made of the same
quantity of resin and having a substantially similar shape, the
strength of the hook is increased remarkably, and necessarily the
front part of the stem and the lower part of the hook-shape
engaging portion are increased in rigidity to hardly deform
compared to the other part, thus causing an increased force of
engagement with loops of the companion surface fastener.
Assuming that the transverse cross section of the hook, which may
have a different shape such as a generally U shape, a generally
inverted T shape or a generally criss-cross shape, has, for
example, a generally criss-cross shape, the strength of hook is
increased and, at the same time, the front part of the stem and the
inner part of the hook-shape engaging portion is increased in
rigidity compared to the other part, thus causing an increased
force of engagement with loops of the companion surface fastener.
Further, when the loop is disengaged from the hook as pulled in a
stretching direction, the loop moves toward the tip of the
hook-shape engaging portion as the hook-shape engaging portion
progressively stands up. During that time, the loop frictionally
presses opposite projections of the criss-cross section of the hook
to deform against their resiliency as the loop gradually moves
toward the tip of the hook. During this moving, the resilience and
frictional force of the opposite ends of the widened part and the
opposite ends of the criss-cross section are exerted on the loop so
that the loop will become difficult to disengage from the hook,
thus causing an increased force of engagement with the loop.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view of a hook according to a typical embodiment
of this invention, with transverse cross-sectional views taken
along lines I--I, II--II and III--III, respectively;
FIG. 2 a front view of the hook of FIG. 1;
FIG. 3 side view of a hook according to a second embodiment of the
invention, with transverse cross-sectional views taken along lines
I--I, II--II and III--III, respectively;
FIG. 4 is a front view of the hook of FIG. 3;
FIG. 5 is a side view of a hook according to a third embodiment of
the invention, with transverse cross-sectional views taken along
lines I--I, II--II and III--III, respectively;
FIG. 6 is a front view of the hook of FIG, 5;
FIG. 7 is a side view of a hook according to a fourth embodiment of
the invention, with transverse cross-sectional views taken along
lines I--I, II--II and III--III, respectively;
FIG. 8 is a front view of the hook of FIG. 7;
FIG. 9 is a transverse cross-sectional view showing a modification
of the hook of FIG. 7;
FIG. 10 is a side view of a hook according to a fifth embodiment of
the invention, with transverse cross-sectional views taken along
lines I--I, II--II and III--III, respectively;
FIG. 11 is a front view of the hook of FIG. 10;
FIG. 12 is a side view of a hook according to a sixth embodiment of
the invention, with transverse cross-sectional views taken along
lines I--I, II--II and III--III, respectively; and
FIG. 13 is a front view of the hook of FIG. 12.
FIG. 14 is a side view of a hook according to a seventh embodiment
tile invention, with transverse cross-sectional views taken along
lines I--I, II--II and III--III, respectively.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Preferred embodiments of this invention will now be described in
detail with reference to the accompanying drawings. FIG. 1 is a
view showing a typical example of hook structure and variation of
transverse cross sections according to this invention. FIG. 2 is a
front view of the hook.
In FIGS. 1 and 2, a hook 10 has a stem 11, which has a rear surface
11a rising obliquely in a smooth curve from a substrate sheet 15
and a front surface 11b rising upwardly from the substrate sheet
15, and a hook-shape engaging portion 12 extending forwardly and
curving downwardly from a distal end of the stem 11. The hook 10
has a varying transverse cross-sectional area progressively
increasing from a tip of the hook-shape engaging portion 12 to a
base of the stem 11. Further, in the illustrated example, the hook
10 has on each of opposite side surfaces a mount-shape reinforcing
rib 13 extending from the base of the stem 11; but such reinforcing
ribs 13 may be omitted. The reinforcing rib 13 may be a multi-step
form so as to have a varying thickness larger toward the base, or
may project upwardly beyond the upper end of the stem 11 and may
terminate short of the upper end of the hook-shape engaging portion
12.
The characteristic feature of the hook 10 resides in the transverse
cross-sectional shape of the stem 11 and the hook-shape engaging
portion 12 in particular. Specifically, in each of a transverse
cross section of the stem 11 parallel to the substrate sheet 15 and
an arbitrary transverse cross section including a normal line at a
lower surface of the hook-shape engaging portion 12, when the
cross-sectional area is divided into front and rear side
cross-sectional areas S1, S2 at the center line as viewed in side
elevation, the front side cross-sectional area S1 is set to be
larger than the rear side cross-sectional area S2. In this
specification, the center line L of the hook 10 is a curve tracing
successive center points of maximum width in either longitudinal or
transverse width of every transverse cross section. Like reference
designate similar parts or elements throughout various embodiments
in the following description. In this invention, the
cross-sectional profile of each of the stem 11 and the hook-shape
engaging portion 12 may be arbitrarily decided. In the illustrated
example, the front surface of the stem 11 gradually rises in a
curve toward the rear side of the substrate sheet 15 and extends
perpendicularly upwardly from the halfway. Alternatively, the front
surface of the stem 11 may rise perpendicularly directly from the
substrate sheet 15.
In the first embodiments of FIGS. 1 and 2, the transverse
cross-sectional shape of each of the stem 11 and the hook-shape
engaging portion 12 is generally trapezoidal. The top side of the
trapezoidal shape defines the rear side of the stem 11 and the
outer side of the hook-shape engaging portion 12, and the bottom
side of the trapezoidal shape defines the front side of the stem 11
and the inner side of the hook-shape engaging portion 12, the
entire transverse cross-sectional area increasing progressively
from the-tip of the hook-shape engaging portion 12 to the base of
the stem 11. Using this cross-sectional shape, the center line of
figure of the hook 10 is located eccentrically toward the front
side of the stem 11 and the inner side of the hook-shape engaging
portion 12. As a result, the neutral surface of the hook 10 is
shifted off the center line of figure to the front side of the stem
11 and the inner side of the hook-shape engaging portion 12 to
reduce possible tensile stresses that occurs both in the front part
of the stem 11 and the inner part of the hook-shape engaging
portion 12 so that, as compared to the conventional hook made of
the same resin quantity and having a substantially similar shape,
the strength of the hook 10 is increased remarkably and, at the
same time, since the front part of the stem 11 and the inner part
of the hook-shape engaging portion 12 are increased in rigidity
compared to the other part, and hence are difficult to deform thus
causing an increased force of engagement with loops of the
companion surface fastener.
FIGS. 3 and 4 show a second embodiment of this invention, in which
the transverse cross-sectional shape is analogous to a
cross-sectional shape taken along the longitudinal axis of an egg.
The small-width side of this eggshape cross section defines the
rear side of the hook 10 while the large-width side of the
egg-shape cross section defines the front side of the stem 11 and
the inner side of the hook-shape engaging portion 12. FIGS. 5 and 6
show a third embodiment of this invention, in which the transverse
cross-sectional shape of the hook 10 is a rhombic shape with two
adjacent sides being shorter than the other two sides and located
in the front side of the stem 11 and the inner side of the
hook-shape engaging portion 12.
FIGS. 7 and 8 show a fourth embodiment of this invention, in which
the transverse cross-sectional shape of the hook 10 is a generally
inverted T shape with the large-width side located the front side
of the stem 11 and the inner side of the hook-shape engaging
portion 12. In this embodiment, the longitudinal (right and left
direction of FIGS. 7) width L1 of the large-width part 10a is set
to be the same along the entire length of the hook 10, and the
thickness L2 of the large-width part 10a increases progressively
from the tip to the base of the hook 10. Of course, The inverted
T-shape cross section may increase analogously from the tip to the
base of the hook 10. Alternatively, as shown in FIG. 9, the
transverse cross-sectional shape may be a generally criss-cross
shape with its opposite side projections 10b located eccentrically
toward each of the front side of the stem 11 and the inner side of
the hook-shape engaging portion 12.
Also according to the fourth embodiment of FIGS. 7 through 9, the
strength of the hook 10 increases remarkably likewise the first and
second embodiments and, at the same time, each of the front part of
the stem 11 and the inner part of the hook-shape engaging portion
12 has an increased degree of rigidness as compared to the other
part, thus causing an increased force of engagement with a loop of
the companion surface fastener. In the fourth embodiment, the force
of engagement with the loop is further increased. Specifically, in
this type surface fastener, when the loop is disengaged from the
hook 10, the loop is pulled in a tensing direction and is moved
toward the tip of the hook-shape engaging portion 12 as it causes
the hook-shape engaging portion 12 of the hook 10 to progressively
stand up. In the hook 10 of this embodiment, during this moving,
the loop frictionally presses the opposite ends of the large-width
part 10a or the opposite projections 10b of the criss-cross section
to deform as it is moved progressively toward the tip of the hook
10. During this moving, the resilience and frictional force of the
opposite ends of the widened part 10a and the opposite ends 10b of
the criss-cross section are exerted on the loop so that the loop
will become difficult to disengage from the hook 10, thus causing
an increased force of engagement with the loop.
FIGS. 10 through 13 show fifth and sixth embodiments, in which the
transverse cross section of the hook 10 has a U shape. In the fifth
embodiment, a generally U-shape groove 10c is located in each of
the rear part of the stem 11 and the outer part of the hook-shape
engaging portion 12 and has a substantially uniform shape along the
entire length of the hook 10. In the sixth embodiment, the U-shape
groove 10c is located in one of the opposite side surfaces (in FIG.
12, left side surface) of the hook 10, having a width W1 gradually
decreasing from the base of the stem 11 to the tip of the
hook-shape engaging portion 12. In the fifth and sixth embodiments,
like the third and fourth embodiments, the strength of the hook 10
is increased remarkably and, at the same time, both the front part
of the stem 11 and the inner part of the hook-shape engaging
portion 12 are increased in rigidity as compared to the other part.
Further, in the grooved region, when the loop moves on the hook 10
in the removing direction, opposite projections 10d of the U-shape
groove 10c will deform as frictionally pressed by the loop so that
the loop is difficult to disengage from the hook 10 due to the
resiliency and frictional force of the opposite projections 10d,
thus causing an increased force of engagement with a loop.
FIGS. 14 shows a seventh embodiment, in which the transverse cross
section of the hook 10 has a triangular shape. In the seventh
embodiment, one of the three angles is situated on the rear side of
the stem 11. With the seventh embodiment, like the foregoing
embodiments, the strength of the hook 10 is increased remarkably,
and at the same time, both the front part of the stem 11 and the
inner part of the hook-shape engaging portion 12 are increased in
rigidity as compared to the other part.
As is apparent from the foregoing description, according to the
hook structure of this invention, in each of a transverse cross
section of the stem along a line parallel to the substrate sheet
and an arbitrary transverse cross section including a normal line
at the lower surface of the hook-shape engaging portion, when the
transverse cross-sectional area is divided into front and rear side
cross-sectional areas, the front side cross-sectional area is set
to be larger than the rear side cross-sectional area. Therefore,
the neutral plane of the hook is shifted toward the front side of
the stem and the inner side of the hook-shape engaging portion to a
further extent than conventional to reduce possible tensile
stresses in the front part of the stem and the inner part of the
hook-shape engaging portion so that, as compared to the
conventional hook made of the same resin quantity and having a
substantially similar shape, the strength of the hook is increased
remarkably and, necessarily, both the front part of the stem and
the inner part of the hook-shape engaging portion have an increased
degree of rigidity as compared to the other part and hence are
difficult to deform, thus causing an increased force of engagement
with a loop of the companion loop.
In the case that the transverse cross section of the hook has a
generally criss-cross shape, a generally inverted T shape or a
generally U shape, when the loop of the companion surface fastener
is moved on the hook as pulled in the removing direction, the
small-thickness part of the hook will resiliently deform as
frictionally pressed by the loop so that the resiliency and
frictional force simultaneously act between the hook and the loop
to cause the loop become difficult to disengage from the hook, thus
causing a further increased force of engagement with the loop.
* * * * *